1. Field of the Invention
The present invention relates to a radiation-curable adhesive composition and an adhesive sheet.
2. Background Information
The radiation-curable adhesive composition facilitates a peeling operation by reducing adhesive characteristics from a state of strong adhesive characteristics as a result of curing by exposure to radiation.
Thus, use is preferred in relation to applications that require the contrary characteristics of strong adhesive performance and ease of peeling. For example, an adhesive sheet is provided with an adhesive layer formed by the above type of radiation-curable adhesive composition, and is adhered to the surface of an adherend to thereby protect and fix that surface. When no longer required, the adhesive characteristics are reduced as a result of curing the adhesive agent by irradiation with radiation of the adhesive sheet attached to the adherend to thereby facilitate peeling by a gentle peeling operation of the adhesive sheet.
In particular, during dicing, an adhesive sheet used for dicing of a semiconductor wafer or the like requires an adhesive force of a level that does not allow peeling from the semiconductor wafer and an adhesive force of a level to prevent detachment from the dicing ring used for retaining the wafer. On the other hand, when executing a pick-up operation after dicing, it is necessary to facilitate peeling with an adhesive force that is sufficiently low to prevent damage to the semiconductor wafer.
As a result, various adhesive sheets have been proposed (for example, see JP2005-19607A and JP2007-220694A).
Furthermore, an adhesive sheet used for dicing requires low contamination characteristics such as avoidance of residual adhesive on the semiconductor wafer, and re-peelable sheets have been proposed in an attempt to meet both these characteristics (for example, JP2001-234136A).
Normally, a pick-up operation after dicing is executed after performance of an expanding step in which the interval between each semiconductor chip is increased. The expanding step is a step of forming a configuration in which peeling of the semiconductor chip from the adhesive sheet used for dicing is facilitated. Furthermore, this step is executed by creating a configuration in which the adhesive sheet for dicing is stretched to a certain extent and the adhesive sheet for dicing at the bottom portion of the semiconductor chip to be picked up is lifted up in a point condition or linear condition (normally termed “raising”). In recent years, a pick-up method has been mainly used in which the semiconductor chip is placed in this type of easily peelable state, and then picked up by vacuum attachment from the upper side.
As described above, the increased reduction in the thickness and weight of the semiconductor product or the increased reduction in the thickness of the semiconductor wafer as a result of enhanced integration has caused an increase in the risk of damage to the semiconductor wafer as a result of a deformation resulting from raising of the adhesive sheet during the pick-up process.
Therefore, there is a need for a method of enabling a safe pick-up operation that does not cause damage to the chip during a slight raising operation.